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[JMauk]

Hi All,
Again, I have been remiss in keeping up with this great site.  Every time I log in I always learn something.  Since posting video on the first rail car test, we have tested full-length runs with no weight and no pulling of top,  half-length runs with full weight and no pulling.  This past week we started testing the pulling of the top, first with no weight on the rail car and then, today (see video) with 300 Kg on the rail car.  We are finding it fascinating that the rail car stops at the bottom of the slope after pulling the top and doesn't even come close to the crash bunker we built.  Wondering what it will be like with the 1,550 Kg weight installed. I'm interested if any of you can give me an idea of the rpm's we reached on this test.  At least on my computer playback, the spin looks slower at first than later on, actual eye visual showed a blurring of the dots at first but the recorded visual shows them not blurring, as though slower than what it really is. Any ideas what is going on there?

[ta0]

Wow! I am truly impressed (again)! You built a major construction around the top!

The reason the dots don't blur in the video is a stroboscope effect between the frame rate and the regular pattern of dots. You can even see them appear to stop and spin backwards. If  you want the details, I wrote an "ultimate guide" to interpreting the camera strobe effect when filming a spintop on this thread: link. It is a pity the camera did not stay on the top so we could follow all the apparent changes. But I will see if I can still come up with an estimate.

Another way of estimating the rotation rate would be from the speed of the cart and the diameter of the spool. Again a camera staying on the cart would have let us time its speed better.

Anyway, that is a great test run!

[Larry D.]

Congratulations Joe, that’s a great looking test run!
You are certainly on the right track. 
Will the sway of the top increase when you put the heavier payload on the rail car and the RPM increase dramatically?

[the Earl of Whirl]

Very impressive.  Wow!  It is spinning quite nicely!!!

[Dick Stohr]

Looking good, love the incremental testing. ALL THE BEST!!!!!!!!

[dazzlingdave]

Very cool!

[ta0]

Fortunately there are scratches on some of the red disks so it is sometimes possible to follow them.
At 44 seconds it takes 4 video frames for a circle to replace a circle 3 spots ahead. Each frame is 1/30 second so that is 4/30 seconds. You have 12 red circles, so 3 spots is 1/4 of a turn. Therefore it takes T = (4/30)x4 = 0.533 sec for one turn and the rotational speed is 1/T = 1.875 Hz x 60 = 112.5 RPM.
However at 44 seconds the weight is already down so the top is already decelerating. Its maximum speed must be the instant the wagon reaches the bottom of the track, but that is not in the video. A little before I measure about 100 RPM.

[Kirk]

Joe,
It is so excellent that you are doing incremental testing.   How long did it spin?

I have a few observations.

I see that the rail cart comes to a near stop a couple of times. My guess is that the cart is waiting for the stretch in the rope to catch up.  You may wish to investigate different rope types.  Nylon rope is very elastic. Poly rope (AKA polyethylene) is even more elastic.  Polyester is quite a bit stiffer. Then of course there are the expensive super ropes like spider line, kevlar and such.
Then again I wonder if the stretch is all that important.
The bottom of this page lists Young's Modulus (stiffness) for various ropes.
http://www-materials.eng.cam.ac.uk/mpsite/short/OCR/ropes/
I was surprised to see how stiff and strong hemp is. (but not weather resistant)

The fact that the cart stops at the bottom of the ramp is rather disconcerting. What happened to all the kinetic energy?  Back to wondering about the rope stretch.

Speed estimates from video are always suspect.  The frame rate of the video will play tricks with the dots.  We use one of these laser tachometers at work. How that make such a good device for less that $20 I do not know.  There is probably a seller closer to you than Amazon.
http://www.amazon.com/CyberTech-Digital-Photo-Tachometer-Contact/dp/B001N4QY66/ref=sr_1_1?ie=UTF8&qid=1410046801&sr=8-1&keywords=tachometer
You would probably need to rig a pole and view the display with a telescope for safety.

[yollector]

   This is just way to cool !
no matter what I want to wish you
  THE BEST OF LUCK  !!!!!!
                   RFC 

[JMauk]

Thanks, guys, it spun about 14 minutes, the first manual spin when brand new March 10, 2012 was 19 minutes.  Have obviously lost some efficiency with age, either in top bearings or wearing of bottom point and plate.  The rpm's seem to be have been a bit faster, from what you have shared, but time of spin shorter.  I think the rope stretch idea might be what is causing the hesitation in the roll and finishing with a stop instead of continued roll.  We are using rappelling rope, very strong, but does stretch.  It looks like it may be using the weight of the top to slow the roll of the cart, like dropping a mountaineer slowly onto a ledge.  Any physics in support of this?

[ta0]

I looked again at the video frame by frame and there is no doubt that  you are getting just a bit over 100 RPM, perhaps 115 max. Given the relatively slow speed and large size, a couple of large dots of different color on the top would make it very easy to measure the RPMs using a camera.

You did not mention the weight of the rail car. Is 300 kg the weight of the rail car plus sand bags or just the sand bags?
I am guessing the later but the most favorable for our calculation would be if it was the total.
With 300 kg 425 kg and 110 RPM your conversion efficiency would have been 81.5%, which is not bad 57.5%.
In theory, getting the weight 5 times larger will give you a spin sqr(5) = 2.2 time faster.

The cart is slowed down by both the energy it gives to the top and the energy lost to friction. If you had 100% conversion to spin it would had arrived with zero velocity to the bottom. Again, using 300 kg for the total weight and a max speed of 110 RPM, and with no loses, the cart should have arrived at the bottom with a speed of 20 km/h and continued with that speed until it hit the barrier. But the friction loses in the system were enough to brake it.

Like Kirk, I am a little concerned about those hesitations of the cart. We already saw what can happen when something gets stuck and there is a jerk in the mechanism. You should strive to get it running smoothly.

[JMauk]

Thanks taO, it all makes sense.  Might experiment with a different rope while weight is still only 20% of full.  And, did you say you were concerned about the jerk in the mechanism or the jerk running the mechanism?  :-D

[jim in paris]

Dear Joe and the Team

first a big thanx to let us share the latest experiment , almost live!
I agree with the remarks and calculation
the huge stand you've built is in itself impressive and the cart on rails works very well...the cart hesitations : too much friction or snags in the winding process could be a clue, but with the full load it might/should disappear

good luck for next attempts 
jim